<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>


    <script>

        // str.charAt(i)   str[i]   通过下标访问字符串的值 
        // str.charCodeAt(i)   返回下标对应的字符的ASCII值
        // String.fromCharCode()   返回ASCII值对应的字符

       

        var str = 'hello' ;
        console.log(str.charAt(0));

        console.log(str.charCodeAt(1));


        console.log(String.fromCharCode(104));


        var smallArr = [] ;
        for(var i = 97 ;  i <= 122 ; i++) {
            var s = String.fromCharCode(i) ;
            smallArr.push(s) ;
        }
        console.log(smallArr);

        var bigArr = [] ;
        for(var i = 65 ;  i <= 90 ; i++) {
            var s = String.fromCharCode(i) ;
            bigArr.push(s) ;
        }
        console.log(bigArr);

        var numArr = [] ;
        for(var i = 0 ; i <= 9 ; i++) {
            numArr.push(i + '') ;
        }

        var allArr = smallArr.concat(bigArr , numArr) ;
        console.log(allArr);




    </script>
    
</body>
</html>